Project Summary/Abstract Regulatory T cells (Tregs) play a major role in establishing and maintaining immune homeostasis. The function of these cells depends on the tissues in which they reside. We have previously shown that both murine and human skin contain a unique population of Tregs; however, the mechanisms utilized by these cells to mediate their functions in this tissue are largely unknown. Using an biased discovery approach, we identified LAYN (layilin), a novel C-type lectin receptor-like molecule, to be preferentially and highly expressed on Tregs in skin in an evolutionarily conserved manner. Layilin has been shown to interact with the extracellular matrix through its extracellular domain and with the actin cytoskeleton through its intracellular domain, suggesting that this molecule facilitates cell mobility and migration within tissues. Expression of layilin on immune cells has not been reported and the function of this protein in the context of tissue inflammation is entirely unknown. The overall goal of this proposal is to elucidate the functional role of layilin expression on Tregs in murine and human skin. We hypothesize that Tregs utilize layilin to localize and/or migrate within skin in the steady-state and/or during inflammation. In doing so, we speculate that this molecule plays a major role in Treg function in this tissue. To test this hypothesis, we have generated mice that are deficient in layilin, as well as systems to overexpress and genetically delete layilin in human Tregs. The experiments outlined herein represent a conceptually and technically innovative, systematic approach to better understand how Tregs utilize a novel molecule to regulate inflammation in skin. Our results may have implications for clinical approaches focused on functionally manipulating tissue-specific Tregs.